The present invention relates to a reusable container that also is a dispensing system for containing, storing and dispensing ultra high purity chemicals.
The storage of ultra high purity liquid chemicals, for example those chemicals having a purity greater than or equal to 99.9999%, is difficult to achieve because vapors and gases from the environment and ions from the storage container itself diffuse into the highly pure chemical. Ultra high purity chemicals are customarily used in the manufacture of semiconductor or integrated circuit chips during a chemical vapor deposition step. Maintenance of the chemical purity during storage, transport and dispensing is critical to the ultimate quality of the finished semiconductor or integrated circuit product. To maintain this purity, a chemical resistant container is required which is impervious to the diffusion of contaminants such as water vapor, oxygen and other vapors and gases. In addition, to minimize exposure to humans during the dispensing process, the container should also include a dispensing apparatus.
Known containers/dispensers for high purity chemicals typically utilize a quartz glass container to maintain the chemical purity during storage and dispensing. However, the use of quartz glass complicates transportation, storage, usage and re-use of the containers.
Quartz glass containers are subject to breakage, leakage and general damage due to the fragile nature of the glass. Breakage may occur at any time and can result in severe injury or death to humans due to chemical exposure by the ultra high purity chemical or contaminate the environment. Further, due to their cost, these quartz glass devices are rebuilt and re-used several times which increases the probability of breakage of the glass due to weakening of the glass container during transportation, handling and reuse.
These quartz glass containers must be retired from service when sophisticated inspection techniques determine that the glass has been damaged, such as by etching or scratching, in order to prevent a complete failure of the glass container. This retirement may occur before the first re-use depending upon how carefully the container was handled during the transport, dispensing, re-transport and refilling operations. Premature retirement results in excessive cost to the vendor and to the ultimate user of the ultra high purity chemical. Due to a high degree of uncertainty and the potential of abuse during handling and transport operations, the inspection of used containers is costly since each container must be approved or recertified before continued service. Vendors and users cannot always be certain of the operating costs and business risks associated with these known devices and, therefore, they may require mandatory retirement at a prescribed time in the life of the quartz glass containers.
One commercially available container/dispenser is called a bubbler since the ultra high purity chemical is dispensed by injecting an inert or non-reactive gas, such as nitrogen, into a liquid phase pure chemical. This inert gas is injected at a lower region in the liquid filled container such that the inert gas bubbles to the surface of the liquid and becomes saturated with the high purity chemical. The level of saturation is based upon the pressure and temperature of the liquid and the ability of the inert gas to "carry" the high purity vapor molecules with it during the bubbling or dispensing process. One commercially available bubbler is manufactured by J. C. Schumacher Co. of Oceanside, Calif. Another bubbler is described in U.S. Pat. No. 4,140,735 to Schumacher. Some of the background details regarding the bubbling of high purity chemicals can be found in that Schumacher patent. Therefore, the Schumacher patent is incorporated herein by reference thereto. Typical high purity chemicals used in the manufacture of semiconductor products are phosphorus oxychloride, boron tribromide, trichloroethane, and others.
U.S. Pat. No. 4,343,413 to Chatzipetros et al. discloses a double walled vessel for dewar flasks wherein an inner glass container is spaced from an outer glass container by rubber-like spacers. U.S. Pat. No. 4,595,112 to Dubois discloses a thermal container having an outer walled container of metal, a thick walled insulating shell and a very thin walled plastic liner. The outer container, thick walled insulating shell and inner liner abut each other, that is, they are not spaced apart but are sandwiched together. U.S. Pat. No. 4,595,113 to Fafflok et al. discloses a container/dispenser having an outer housing made of plastic, a secondary double walled intermediate container of glass, plastic or similar material and an inner container. The inner container, double walled intermediate container, and outer container are all spaced apart and are maintained in a spaced relationship due to upper lips coacting together.
A study has analyzed the possibility of using "TEFLON" like material for containing ultra high purity chemicals. This study measured the permeability of TEFLON perfluoroalkoxy (PFA) polymer. The results of this study by J. C. Schumacher Co. indicate that the TEFLON polymer is permeable by water vapor. Based on this published study, it was thought TEFLON polymer would not be suitable for storing and maintaining the integrity of high purity chemicals. Very recently, Nalge of Rochester, N.Y. announced a new container for storing reactive and high purity chemicals made of teflon PFA. The TEFLON fluoropolymer's resistance was stated as being ideal for fluorine-fluoride chemistry.